1. Field of the Invention
The present invention relates to a power converting apparatus for performing conversion between DC power and AC power by using a plurality of semiconductor switching devices and, more particularly, to a power converting apparatus configured to operate by pulse-width modulation (PWM) control operation while detecting a plurality of phase currents.
2. Description of the Background Art
A conventional arrangement for increasing an output of a power converting apparatus is to use a multiplex inverter in which a plurality of three-phase inverters are connected in parallel. This kind of multiplex inverter is provided with three-phase inverters each including three current detectors and operates by PWM control while detecting individual phase currents (refer to Japanese Patent No. 4625147 and Japanese Patent Application Publication No. 2011-131860, for example).
A conventional arrangement for detecting phase currents of a three-phase inverter is as follows. A power converting apparatus repeatedly executes inverter control operation at intervals of an inverter control period having a specific length. A phase current detection period during which the phase currents are detected is provided between successive inverter control periods. The power converting apparatus controls switching states of individual switching devices of inverter circuits so that a shunt resistor outputs a voltage pulse having a pulse duration larger than that of a voltage pulse output during the inverter control period during each phase current detection period (refer to Japanese Patent No. 4671000, for example).
The conventional multiplex inverter like those of Japanese Patent No. 4625147 and Japanese Patent Application Publication No. 2011-131860 cited above is provided with a plurality of three-phase inverters each including three current detectors. Thus, the total number of the current detectors required in each of such multiplex inverters is three times the number of the three-phase inverters. A problem of this arrangement is therefore an increase in size of the apparatus associated with an increase in manufacturing cost.
In the power converting apparatus described in Japanese Patent No. 4671000 cited above which is configured to detect the individual phase currents by using a single current detector, an output voltage of the current detector is kept at a fixed level during each phase current detection period. A problem of this arrangement is that voltage and current output waveforms can be distorted if the output voltage deviates from a desired voltage.